The present invention relates to a device for carrying out mechanical, chemical and/or thermal processes in a housing comprising mixing and cleaning elements on shafts, wherein the mixing and cleaning elements of the shafts engage into one another when they rotate about the axes thereof, and two axially successive mixing and cleaning elements are arranged at least on one shaft respectively such that they are rotationally symmetrical by about 180° in relation to one another about the axis of the shaft thereon.
Such devices are also referred to as mixing kneaders. They serve for a wide variety of different purposes. To be mentioned first is evaporation with solvent recovery, which is performed batchwise or continuously and often also under a vacuum. By way of example, this is used for treating distillation residues and, in particular, toluene diisocyanates, but also production residues with toxic or high-boiling solvents from the chemical industry and pharmaceutical production, wash solutions and paint sludges, polymer solutions, elastomer solutions from solvent polymerization, adhesives and sealing compounds.
The apparatuses are also used for carrying out continuous or batchwise contact drying of water-moist and/or solvent-moist products, often likewise under a vacuum. Intended applications are in particular for pigments, dyes, fine chemicals, additives, such as salts, oxides, hydroxides, antioxidants, temperature-sensitive pharmaceutical and vitamin products, active substances, polymers, synthetic rubbers, polymer suspensions, latex, hydrogels, waxes, pesticides and residues from chemical or pharmaceutical production, such as salts, catalysts, slags, waste liquors. These processes also find applications in food production, for example in the production and/or treatment of block milk, sugar substitutes, starch derivatives, alginates, for the treatment of industrial sludges, oil sludges, bio sludges, paper sludges, paint sludges and generally for the treatment of tacky, crust-forming viscous-pasty products, waste products and cellulose derivatives.
In mixing kneaders, degassing and/or devolatilization can take place. This is applied to polymer melts, after the condensation of polyester or polyamide melts, to spinning solutions for synthetic fibers and to polymer or elastomer granules or powders in the solid state.
In a mixing kneader, a polycondensation reaction can take place, usually continuously and usually in the melt, and is used in particular in the treatment of polyamides, polyesters, polyacetates, polyimides, thermoplastics, elastomers, silicones, urea resins, phenolic resins, detergents and fertilizers.
A polymerization reaction can also take place, likewise usually continuously. This is applied to polyacrylates, hydrogels, polyols, thermoplastic polymers, elastomers, syndiotactic polystyrene and polyacrylamides.
Quite generally, solid/liquid and multi-phase reactions can take place in the mixing kneader. This applies in particular to back-reactions, in the treatment of hydrofluoric acid, stearates, cyanates, polyphosphates, cyanuric acids, cellulose derivatives, cellulose esters, cellulose ethers, polyacetal resins, sulfanilic acids, Cu-phthalocyanines, starch derivatives, ammonium polyphosphates, sulfonates, pesticides and fertilizers.
Furthermore, solid/gas reactions can take place (for example carboxylation) or liquid/gas reactions can take place. This is applied in the treatment of acetates, azides, Kolbe-Schmitt reactions, for example BON, Na salicylates, parahydroxybenzoates and pharmaceutical products.
Liquid/liquid reactions take place in the case of neutralization reactions and transesterification reactions.
Dissolution and/or degassing takes place in such mixing kneaders in the case of spinning solutions for synthetic fibers, polyamides, polyesters and celluloses.
What is known as flushing takes place in the treatment or production of pigments.
A solid-state post-condensation takes place in the production or treatment of polyesters and polyamides, a continuous slurrying, for example in the treatment of fibers, for example cellulose fibers, with solvents, crystallization from the melt or from solutions in the treatment of salts, fine chemicals, polyols, alkoxides, compounding, mixing (continuously and/or batchwise) in the case of polymer mixtures, silicone compounds, sealing compounds, fly ash, coagulation (in particular continuously) in the treatment of polymer suspensions.
In a mixing kneader, multi-functional processes can also be combined, for example heating, drying, melting, crystallizing, mixing, degassing, reacting-all of these continuously or batchwise. Substances which are produced or treated by this means are polymers, elastomers, inorganic products, residues, pharmaceutical products, food products, printing inks.
In mixing kneaders, vacuum sublimation/desublimation can also take place, whereby chemical precursors, for example anthraquinone, metal chlorides, organometallic compounds etc., are purified. Furthermore, pharmaceutical intermediates can be produced.
A continuous carrier-gas desublimation takes place, for example, in the case of organic intermediates, for example anthraquinone and fine chemicals.
A mixing kneader of the type mentioned above is known from EP 0 517 068 B1, for example. In it, two shafts extending axially parallel rotate in a counter-rotating or co-rotating manner in a mixer housing. In this case, mixing bars mounted on disk elements act with one another. Apart from the function of mixing, the mixing bars have the task of cleaning as well as possible surfaces of the mixer housing, of the shafts and of the disk elements that are in contact with the product and of thereby avoiding unmixed zones. Particularly in the case of highly compacting, hardening and crust-forming products, the ability of the mixing bars to reach the edges leads to high local mechanical loading of the mixing bars and of the shafts. These force peaks occur in particular when the mixing bars engage in those zones where the product finds it difficult to escape. Such zones are present, for example, where the disk elements are mounted on the shaft.
Furthermore, DE 199 40 521 A1 discloses a mixing kneader of the type mentioned above, in which the carrying elements form a recess in the region of the kneading bars in order that the kneading bar has the greatest possible axial extent. Such a mixing kneader has outstanding self-cleaning of all the surfaces of the housing and of the shafts that come into contact with the product, but has the characteristic that the carrying elements of the kneading bars require recesses on account of the paths of the kneading bars, leading to complicated forms of the carrying elements. One result of this is a complex production process and another result is local stress peaks at the shaft and the carrying elements under mechanical loading. These stress peaks, which occur primarily at the sharp-edged recesses and changes in thickness, in particular in the region where the carrying elements are welded onto the core of the shaft, are causes of cracks in the shaft and the carrying elements as a result of material fatigue.
A distinction is substantially made between single-shaft and dual-shaft mixing kneaders. A multi-shaft mixing and kneading machine is described in CH-A 506 322. In this machine, radial disk elements and axially oriented kneading bars arranged between the disks are located on a shaft. Mixing and kneading elements shaped in a frame-like manner engage between said disks from the other shaft. These mixing and kneading elements clean the disks and kneading bars of the first shaft. The kneading bars on both shafts in turn clean the inner wall of the housing.
These known dual-shaft mixing kneaders have the disadvantage that, owing to the eight-shaped housing cross section, they have a weak point in the region in which the two shaft housings are connected. In this region, high stresses are produced during the processing of tough products and/or during processes which proceed under pressure, and these stresses can only be controlled by complex design measures.
Further problems of the dual-shaft machines are known in respect of                sealing of the shafts against pressure or seals for an extremely low vacuum,        explosion protection of the housing,        accuracy of concentric running in the housing, and        sealing of the housing.        